I would encourage him/her to acclimatize his/her stomach as fast as possible by diving straight into the local cuisine, for which I’d recommend Jahangir, a clean and bustling restaurant which serves good local food. I would also recommend Kabul Restaurant which serves great Afghani barbeque. After a few initial days of runny tummy they’d be hooked onto spicy food for the rest of their lives.

For more information on local restaurants, check out Islamabad’s WikiTravel page: